Photo-electric tube



Sept. 22, 1931.

F. SCHROTER 1,824,573

PHOTO-ELECTRIC TUBE ,Filed May 15 1926 ENTQR Fm scmzom AT RNEY Patented Sept. 22, 193i UNITED STATES PATENT" VOFFICEE FRITZ SCHBbTEB, OF BERLIN, GERMANY, ASSIGNOR TO GESELLSCHAFT EUR DRAHT-. LOSE TELEGRAPHIE I. B. H 01' BERLIN, GERMANY, A CORPORATION OF GEBHANY ZPHOTO-ELECTRIC TUBE Application med Kay 13, 1928, eria1 K0. 108,91 1, and in'Germany' July 8 1925.

The object of my invention is to produce a photo-electric cell of increased sensitivity. It is well known that alkali metals can be used for the photo-sensitive electrodes, and that the cells so made are filled with rare gases at reduced pressure. It has also been suggested to use caesium or rubidium for these photo-sensitive electrodes. However, the handling of such easily oxidizable alkali l0 metals is rather diflicult and dangerous, not

to speak of the fact that they are quite expensive, with the result that rubidium or caesium cells were found to be very costly, and their manufacture was attended with great diificulty.

According to my invention, these drawbacks are obviated for the reason that ihe said alkali metals are added only incomparatively small proportions to another basic metal, for instance, potassium, which canbe handled more easily and which is less costly;

Now making reference to the accompanymg drawing 1 denotes the cell vessel provided with the tube 2 leading to an exhaust pump of an desired character. The portion of the tu e 2 shown as 3 is the last sealing point of the trbe. In the appendage or extension 4 of the cell vessel 1 is placed the potassiumcaesium or potassium-rubidium amalgam or alloy which has reviously been absorbed in a glass tube 5 an which is to be distilled over 'into the externally cooled silver coat 6 of the cell wall. The alkali glassv cartridge 5 is preferably of tubular shape so that it may easily be fitted into'the appendage 4. The silver coating 6 of the cell wall is provided with a lead-in wire 7 to which the negative lead may be connected. After covering the silver coating 6. with the alkali-metal alloy, the portion 6 will constitute the photo-active electrode. The annular anode member 9 is connected with the positive lead-in wire 8 in any appropriate manner and this lead-in wire as is the case with the lead-in 7 is appropriately suchas is well known in the art of constructing vacuum tubes. 65

Small additions of a mixture of caesium and rubidium, preferably in proportion to their atomic weights, to potassium, or to the well-known readily fusible alloy of potassium and sodium have also been found very elf- 60' ficient. 1

The treatment of the photo-electrically sensitive surface in the cell (purification, hydration, evacuation, etc.) is accomplished ac-. cording to well-known methods. It has been found that a filling of rare gas under reduced pressure is particularly suitable. Especially very pure helium is advantageous, since by means of helium it has been found possible to raise the critical potential at which the 7 glow-discharge in the cell is initiated, to a comparatively high value, with the result that considerable acceleration potentials for the photo-electrically produced electrons can be worked with. Accordingly, I may term the caesium and rubidium, or the like, accelerators.

The action of an addition in relatively small quantities of photo-electric accentuating metals which may include caesium and rubidium, or both, to the basic metal, looked at from a chemical viewpoint, consists in that the speed of oxidation of the addition metals is markedly diminished, whereby their dangerousness, ignitibleness, reactivity, etc., are correspondingly reduced. From a physical viewpoint, apart from an increase in,v photo-electric sensitivity, it has also been observed'that the limit of the photo-electric effect is shifted in the direction of the longer '9 waves, and this feature can also be usefully employed. Also small additions of other photo-electric accentuating metals. such as zinc, or cadmium, furthermore mercury, produce a favorable effect.

While I have defined my invention in the claimsas directed to the use of caesium in connection with the basic alkali-metal which forms the electrode, i is to be understood that it is fully within the s mpe of my disclosure to include the use of such other metals as rubidium, zinc, cadmium or mercury with the basic alkali-metal so as to considerably aid the photo-electric efiect.

Having described my invention, I claim: 1. A photo-electric cell provided with a light sensitive cathode and an anode member,

said light sensitive cathode being formed of an alkali metal to which a very small portion of caesium is added for the purpose of accentuating the photo-electric efi'ect and raising the critical potential at which glow discharge is started.

2. A photo-electric cell, comprising, a light sensitive cathode member formed of an alkali metal including potassium and a small percentage of caesium, and an anode member for cooperating with said cathode.

3. The photo-electric cell claimed in claim 2 in combination with a filling highly purified helium gas.

4. A photo-electric cell, including, an air tight envelope filled with highly purified helium gas, a photo sensitive cathode member positioned within said envelope, said cathode being formed of a potassium alloy including three percent caesium, and an anode member also positioned within said envelope for cooperating with said cathode.

5. In a photo-electric cell, a cathode formed of a photo-electric element and a small percentage of caesium for serving as an accelerator.

FRITZ soHRoTER. 

